In exploration and production operations for natural resources such as hydrocarbon-based fluids (e.g., oil and natural gas), a wellbore may be drilled into a subterranean formation. If the wellbore comes into contact with a fluid reservoir, the fluid may then be extracted. In some cases, a primary wellbore may be drilled, and additional, deviated boreholes may be formed to extend laterally or at another incline from the primary wellbore. For instance, another wellbore may be drilled to the downhole location of an additional fluid reservoir or to increase production from a fluid reservoir. In creating the deviated borehole, a whipstock may be employed in a method referred to as sidetracking.
A whipstock may have a ramp surface that guides a mill away from a longitudinal axis of the primary wellbore. To create the deviated borehole, the whipstock can be set at a desired depth and the ramp surface oriented to provide a particular trajectory to facilitate a desired drill path. After setting the whipstock, the mill can be moved in a downhole direction and along the ramp surface of the whipstock, and the ramp surface will guide the mill into the casing of a cased wellbore. As the mill is rotated, the mill can grind away the casing and form a window through the casing for access to the surrounding subterranean formation. After formation of the window, the mill can be tripped out of the primary wellbore, and a drill bit can be tripped into the primary wellbore, through the window, and rotated to drill the subterranean formation and follow a desired trajectory.